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D F Ollis

Publications and source records attributed to D F Ollis.

7 recordsLinked to original sources
PubMed1986

A structured model for immobilized cell kinetics.

An intrinsic, structured model has been formulated to describe the kinetics of viable (living) cells immobilized within porous supports. Predictions of steady-state internal biomass concentration distributions, biocatalyst substrate profiles, and immobilized cell growth and leakage from the support are in qualitative agreement with the literature. Simulation studies indicate that carrier pore structure is a particularly important design variable to be optimized.

Catalysis↗
PubMed1975

Hydrolysis of particulate tributyrin in a fluidized lipase reactor.

Pancreatic lipase has been immobilized onto stainless steel beads by adsorption followed by crosslinking, and onto polyacrylamide by covalent bonding. The activities of the two types of immobilized enzyme toward the particulate substrate, tributyrin emulsion droplets, were determined experimentally, and rate constants based on Michaelis-Menten kinetics were calculated. The activity of the stainless steel-lipase was determined for various flow conditions and for various support sizes by the use of a differential fluidized bed recycle reactor. The rate constants calculated indicate that the experimental reaction rate is free from mass transfer influences, since the observed Michaelis constant does not vary with the fluidization velocity or with the support particle size. In addition, the Michaelis constant of the stainless steel-lipase was found to be equal to that of the free enzyme, suggesting that adsorption and subsequent crosslinking does not alter the enzyme-substrate affinity. The emulsion substrate mass transfer rates, calculated from the filtration theory, indicate that each substrate particle which contact the immobilized enzyme is hydrolyzed to a significant extent. The experimentally determined kinetic rate constants may be used directly to predict the size of integral fluidized bed reactors.

Acrylamides↗
PubMedDate not supplied

Enhanced antibody production at slowed growth rates: experimental demonstration and a simple structured model.

A simple structured model for monoclonal antibody (MAb) production kinetics was formulated by combining the cell cycle theory with the estimated number of MAb-coded messenger RNA (mRNA) molecules per cell: it is assumed that the rate-controlling step is first order in this mRNA and that the growth rate variation does not alter the MAb synthesis rate within any cycle phase but only changes the relative time length of the individual phases. The model predicted "negatively growth associated" MAb production kinetics and thus an enhanced MAb production rate to be achieved by slowing the cell growth. Experiments consistent with these assumptions provided support for the model. Hybridoma cultures where growth was slowed by either a DNA synthesis inhibitor (thymidine or hydroxyurea) or by a selective inhibitor of initiation of nonantibody protein (potassium acetate) exhibited 50-130% MAb production rate enhancement for growth slowed up to 50%; however, further decreases in the growth rate also decreased the MAb production rate. Experiments inconsistent with these assumptions showed other behavior: general inhibition of protein chain elongation (by cycloheximide) or inhibition of ribosomal RNA (rRNA) synthesis (by actinomycin D) each slowed both growth and the specific MAb production rate, leading to net "positive" growth associated MAb production rates. Thus, a need for models with greater structure is also demonstrated.

Animals↗
PubMedDate not supplied

Lambda vectors for stable cloned gene expression.

The bacteriophage lambda offers a unique opportunity concurrently to minimize segregational instability in recombinant systems by chromosomal integration of the cloned gene and to achieve high cloned gene expression during an abortive lytic phase. Lysis leads approximately to a 100-fold amplification of the cloned gene. Cell lysis in the lytic state is blocked by a specific mutation (Sam), allowing the cell to maintain its integrity, and lambda DNA packaging is blocked by other mutations (Wam, Eam) that keep cloned genes open to transcription. In the presence of these mutations, extremely high levels of cloned beta-galactosidase (more than 15% of total cell protein) have been obtained during abortive lysis from vectors found to be essentially 100% stable for over 75 generations in the lysogenic phase.

Bacteriophage lambda↗